1. Field of the Invention
The present invention relates to an imaging apparatus configured to perform imaging in a specific direction by driving a pan/tilt head, and a pan/tilt head control method.
2. Description of the Related Art
Monitoring camera systems have been made available which monitor images and control cameras by remote control via a network and a dedicated line in order to prevent crime and to ensure safety. Such a system remotely controls a camera so as to control not only the auto-focus (AF), zoom, exposure, white-balance, resolution, and imaging frame-rate of the camera but the photographing direction of the camera supported by a pan/tilt head.
An example of application of such a monitoring camera system is a real-time manned image monitoring system. In this case, an observer can freely control a pan/tilt head in a tilting direction and in a panning direction from a remote location while observing an image displayed on a monitor, such as a personal computer (PC) monitor or a television (TV) monitor, in real time. Consequently, a desired photographing angle and a desired angle of view can be obtained. An observer can monitor an object by quickly switching scenes of the object by preliminarily registering a plurality of preset positions respectively corresponding to a set of a predetermined photographing direction and a predetermined angle of view.
Another example of application of such a monitoring camera system is a real-time unmanned image monitoring system. In this case, the system automatically photographs still images and moving images with a camera. Then, the system transmits the photographed images to a remote location and records the photograph images in a video tape recorder or a hard disk recorder placed at the remote location. The system can record, while switching scenes, photographed images by changing photographing conditions, such as a photographing direction, to preset conditions corresponding to preset positions at preset specific times or at regular time intervals.
In a case where a pan/tilt head is iteratively moved, enhancement of precision in stopping the pan/tilt head is required. Japanese Patent Application Laid-Open No. 2003-98576 discusses an imaging apparatus that registers preset positions together with images respectively corresponding the preset positions and that compares an actual image, which is photographed when stopping the pan/tilt head at each preset position, with the image registered corresponding to the associated preset position so as to correct an image deviation amount at each preset stopping position.
However, the above-described imaging apparatus has some disadvantages. Generally, accurate positioning control can be easily achieved using a stepping motor. Accordingly, a stepping motor is used in a drive mechanism of the pan/tilt head so as to perform fine control of the position of the pan/tilt head. In the case of using a stepping motor, the positioning control of the absolute position of the pan/tilt head is performed by counting drive pulses of the stepping motor and using a specific initial position as a reference position.
Nevertheless, in the case of the pan/tilt head using a stepping motor, for example, when the pan/tilt head is intentionally and manually moved, or when the pan/tilt head is caught in something, the initial position is changed, thereby throwing off the count value of drive pulses of the stepping motor. Accordingly, the designation of the absolute position of the pan/tilt head may become considerably inaccurate. Particularly, the photographing direction of the camera supported by the pan/tilt head, which is placed within arm's reach, is highly likely to be intentionally changed.
When the designation of the absolute position of the pan/tilt head becomes considerably inaccurate, an amount of deviation of the position of the pan/tilt head cannot be detected. Consequently, the image deviation position at each stopping position of the pan/tilt head of the conventional imaging apparatus cannot be corrected.
In addition, not only in the case where the pan/tilt head is automatically moved to the preset position, but in a case where the pan/tilt head is manually and freely controlled, it is necessary to detect that the position of the pan/tilt head is considerably deviated.